A dental handpiece generally has a head section having a rotary shaft to which a dental tool is attached, a neck section of a generally cylindrical shape extending proximally from the head section and having a drive transmission shaft extending therein, and a grip section of a generally cylindrical shape detachably connected to the proximal end of the neck section and having a rotary shaft extending therein. A drive unit having a motor is detachably connectable to the proximal end of the grip section to operatively link the motor to the rotary shaft. The motor drives the rotary shaft in the grip section, and via the drive transmission shaft in the neck section, rotates the rotary shaft in the head section at a high speed. Some types of such dental handpieces are configured such that the neck section and the grip section are detachably connected via a various kinds of connecting means, and the neck section, the drive transmission shaft, and the grip section may be disassembled for maintenance, such as cleaning.
FIG. 10 shows an example of such a conventional handpiece. In this handpiece 7, the neck section 72 and the grip section 73 are detachably connected via a cylindrical coupling member 74. The coupling member 74, for example as shown in JP-5-23352-A, has on the inner surface in its distal portion a notch engageable to a projection provided in the proximal end portion of the neck section, and on the inner surface in its proximal portion an internal thread to be meshed with an external thread provided on the circumferential surface of the distal portion of the grip section. The neck section 72 and the grip section 73 are assembled by inserting the proximal end of the neck section 72 into the distal end of the grip section 73, and rotating the coupling member 74 clockwise (as seen proximally from the neck section 72) to tighten the threads. In reverse, the neck section 72 and the grip section 73 are disassembled by rotating the coupling member 74 counterclockwise (as seen proximally from the neck section 72) to sufficiently loosen the threads as shown in FIG. 10(A), and pulling apart the neck section 72 and the grip section 73 in the axial direction as shown in FIG. 10(B). Such a coupling member 74 can securely fix the neck section 72 and the grip section 73.
However, with such a connecting mechanism between the neck section and the grip section of the conventional handpiece, the assembly/disassembly of the neck section and the grip section requires repeated screwing up/down of the threaded coupling member, which is laborious and inconvenient. In addition, users have different powers to tighten the coupling member, and in some cases the coupling member may not be tightened sufficiently and may be accidentally rotated and loosened due to the vibration occurring during use of the handpiece.